Pressure measurement guidewires have been in existence since at least the last ten years. These guidewires are most commonly used to measure pressures distal to a lesion, most commonly in the coronary vasculature. By calculating the ratio between the measured pressure distal to the lesion and some point more proximal, most commonly in the ascending aorta or the coronary tree root, the fractional flow reserve (FFR) is obtained. The FFR is now commonly used to assess the degree of lesion stenosis and thereby informs the physician as to the most appropriate treatment strategy. Recently there has been greater clinical acceptance of the importance of measuring translesional pressure gradients and calculating FFR prior to deciding whether to place a stent. As detailed in Pijls et al. “Percutaneous Coronary Intervention of Functionally Nonsignificant Stenosis 5-Year Follow-Up of the DEFER Study.” J Am Coll Cardiol (2007) vol. 49 (21) pp. 2105-2111, which is hereby incorporated by reference, stenting a vessel with an FFR greater or equal to 0.75 does not lead to better outcomes compared to non stenting. Another recent study detailed in Fearon et al. “Rationale and design of the fractional flow reserve versus angiography for multi-vessel evaluation (FAME) study.” American Heart Journal (2007) vol. 154 (4) pp. 632-636, which is also hereby incorporated by reference, a multi-center multi-lesion disease, had a similar conclusion suggesting that not stenting an FFR greater or equal to 0.80 lesion leads to better outcomes. It is expected that FFR will soon become the standard of care to document lesion gradient and determine whether a stent is appropriate.
A common method of measuring the pressure distal to the lesion is through the use of a specialized guidewire with pressure sensors mounted in the guidewire. This is exemplified by the devices described in U.S. Pat. Nos. 6,167,763; 6,112,598 and 6,565,514. These types of devices are now commonly used in coronary vasculature, although their use is not limited to the coronary arteries and they could be used in other vessels of the body. These guidewires serve a double function of pressure measurement to obtain FFR, while at the same time, are used in a fashion similar to standard guidewires, to deliver balloon angioplasty and/or stent therapeutic devices to the diseased plaque location.
Because of this double function, the pressure measuring guidewires necessarily have a more complex construction than standard guidewires used in percutaneous coronary interventions to guide therapeutic devices to the coronary tree. Because of this more complex construction, current guidewires with an embedded pressure sensor have handling and other characteristics which are sub optimal. With the constraints for receiving a pressure sensor such as the use of hollow tubing, the design of a guidewire with adequate handling characteristics leads to limited performances. They have inferior lesion crossing characteristics, are more difficult to place in position and have inferior pushability and torquability characteristics. Physicians accept these inferior handling characteristics as the necessary compromise in order to be able to perform pressure measurements and FFR calculations with the same guidewire used to deliver stent and balloon devices.
Accordingly a need exists for an improved pressure measurement catheter to measure FFR while allowing the physician to use a standard guidewire with optimal handling characteristics.